METHOD FOR DEPOSITING A FLUORINATED LAYER FROM A PRECURSOR MONOMER

PROCEDE POUR DEPOSER UNE COUCHE FLUOREE A PARTIR D'UN MONOMERE PRECURSEUR

English Abstract

The present invention relates to a method for
depositing a fluorinated layer on a substrate, comprising the
injection of a gas mixture including a fluorinated compound
and a carrier gas in a discharge or post-discharge area of a
cold atmospheric plasma at a pressure comprised between 0.8
and 1.2 bars, characterized in that said fluorinated compound
has a boiling temperature at a pressure of 1 bar above 25°C.

French Abstract

La présente invention se rapporte à un procédé pour déposer une couche fluorée sur un substrat, comprenant l'injection d'un mélange gazeux comportant un composé fluoré et un gaz porteur dans une zone de décharge ou de post-décharge d'un plasma froid atmosphérique à une pression comprise entre 0,8 et 1,2 bar, caractérisé en ce que ledit composé fluoré a une température d'ébullition à une pression de 1 bar supérieure à 25°C.

Claims

13
REVENDICATIONS
1. A method for depositing a fluorinated layer on
a substrate, comprising the injection of a gas mixture
including a fluorinated compound and a carrier gas in a
discharge or post-discharge area of an atmospheric plasma at a
pressure comprised between 0,8 and 1,2 bars,
characterized in that said fluorinated compound has a boiling
temperature at a pressure of 1 bar above 25°C.
2. The method according to claim 1 comprising the
steps of:
- bringing the carrier gas into contact with
the liquid fluorinated compound;
- saturating said carrier gas with vapor of
said fluorinated compound in order to form a gas mixture;
- bringing said gas mixture into the discharge
area of an atmospheric plasma;
- placing a substrate in the discharge or
post-discharge area of said atmospheric plasma
characterized in that said fluorinated compound
does not comprise any oxygen or hydrogen.
3. The method according to claim 1 or 2,
characterized in that said method does not comprise any
plasma-free post-treatment.
4. The method according to any of the preceding
claims, characterized in that the fluorinated compound is a
compound selected from the group consisting of C6F14, C-7F16,
C8F18, C9F20 and C10F22 or a mixture thereof.
5. The method according to claim 4, characterized
in that the fluorinated compound is perfluorohexane.
6. The method according to any of the preceding
claims, characterized in that the fluorinated compound is of
the type:

14
<IMG>
wherein R1, R2 and R3 are groups of the
perfluoroalkane type, of formula C n F2n+1.
7.The method according to claim 6, characterized
in that said fluorinated compound comprises
perfluorotributylamine ((C4F9)3N).
8. The method according to any of the preceding
claims, characterized in that the vapor pressure of said
fluorinated compound at room temperature is comprised between 1
mbar and 1 bar.
9. The method according to claim 8, characterized
in that the vapor pressure of said fluorinated compound at room
temperature is comprised between 0.5 mbars and 10 mbars.
10. The method according to any of the preceding
claims, characterized in that the partial pressure of said
fluorinated compound in said carrier gas is regulated by
controlling the temperature of a bath of said fluorinated
compound into which the carried gas is injected before
injection into the plasma.
11. The method according to claim 10,
characterized in that the temperature of the bath is maintained
at a temperature at which the vapor pressure of said compound
is les than 10 mbars.
12. The method according to any of the preceding
claims, characterized in that said atmospheric plasma is
produced by a device of the dielectric barrier type.
13. The method according to any of the preceding
claims, characterized in that said atmospheric plasma is
produced by a device of the type using microwaves.
14. The method according to any of the preceding
claims, characterized in that the substrate comprises a
deposition surface comprising a polymer.

15
15. The method according to claim 14,
characterized in that the substrate comprises a deposition
surface comprising polyvinyl chloride or polyethylene.
16. The method according to any of the preceding
claims, characterized in that the substrate comprises a
deposition surface comprising a metal or a metal alloy.
17. The method according to claim 16,
characterized in that the substrate comprises a deposition
surface comprising steel.
18. The method according to any of the preceding
claims, characterized in that the substrate comprises a
deposition surface comprising glass.

Description

CA 02698629 2010-03-05
1
Office Van Malderen
Bxl - 26 fevrier 201012f6T ri^ 2010
BP.ULBB.137C/WO - ENGLISH VERSION
Couche fluoree
Method for depositing a fluorinated layer from
a precursor monomer
Field of the invention
[0001] The invention relates to the deposition of thin
layers of hydrophobic compounds at the surface of a substrate.
State of the art
[0002] Modifications of surfaces in order to impart new
properties to them are customary things. In this approach, in
order to make anti-adhesive surfaces (including towards
proteins) dirt-repellent or further (ultra)hydrophobic, it is
common to deposit at the surface of the latter a layer,
totally or partly consisting of fluorinated molecules.
[0003] These methods are presently mainly achieved by
the PACVD (plasma assisted chemical vapor deposition) or PECVD
(plasma enhanced chemical vapor deposition) technique. The
usual technique consists of injecting into a plasma reactor,
operating at low pressure, a fluorinated gas monomer (CF4 being
the simplest, but many alternatives exist, such as C2F6, C3F8,
C4F8, fluoroalkylsilanes, etc....) .
[0004] The type of plasma used (RF, microwave plasma, ...)
differs depending on the studies, but the principle remains
the same. The precursor is activated in the low pressure
discharge and plasma polymerization takes place in the gas
phase or at the interface. The main limitation in these
techniques lies in the fact that they imperatively take place
at low pressure (under vacuum).
[0005] Document US2004/0247886 describes a film
deposition method, in which a plasmagenic gas is put into

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contact with a gas comprising a reactive fluorinated compound
in the post-discharge area of an atmospheric plasma, the
plasmagenic gas being injected alone into the plasma area. The
major drawback of this type of method is that it requires the
use of sufficiently reactive compounds. Most of these reactive
compounds then have the drawback either of directly bearing
hydrophilic polar groups, or of reacting in the long term with
atmospheric oxygen or humidity, generating polar groups, and
therefore reducing the hydrophobicity of the surface.
[0006] Generally, a limitation of most of these
techniques is that they require the use of extremely reactive
gases and therefore dangerous to transport, store and handle.
These gases are also strong generators of greenhouse gas
effects and their use is controlled by the Kyoto protocol.
These constraints contribute to limiting depositions of
fluorinated layers to products with high added value.
Objects of the invention
[0007] The object of the present invention is to propose
a method for depositing a fluorinated layer from a precursor
monomer which avoids the drawbacks of existing methods. In
particular, it attempts to avoid the requirement of operating
at reduced pressure. Its object is also to allow the use of
liquid monomers which are easier to handle than gas monomers
and often less controversial on the toxicological and
environmental level.
Summary of the invention
[0008] The present invention relates to a method for
depositing a fluorinated layer on a substrate, comprising the
injection of a gas mixture including a fluorinated compound
and a carrier gas in a discharge or post-discharge area of a
cold atmospheric plasma at a pressure comprised between 0.8
and 1.2 bars, characterized in that said fluorinated compound
has a boiling temperature at a pressure of 1 bar above 25 C.

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[0009] By atmospheric plasma >> or, << cold atmospheric
plasma >> is meant a partly or totally ionized gas which
comprises electrons, (molecular or atomic) ions, atoms or
molecules, and radicals, far from thermodynamic equilibrium,
the electron temperature of which is significantly higher than
that of the ions and of the neutrals, and the pressure of
which is comprised between about 1 mbar and about 1,200 mbars,
preferentially between 800 and 1,200 mbars.
[0010] In a preferred embodiment of the present
invention, the method comprises the steps of:
- bringing the carrier gas into contact with the
liquid fluorinated compound;
- saturating said carrier gas with vapor of said
fluorinated compound in order to form a gas mixture;
- bringing said gas mixture into the discharge area
of an atmospheric plasma;
- placing a substrate in the discharge or
post-discharge area of said atmospheric plasma.
[0011] Preferably, said fluorinated compound does not
comprise any hydrogen atom or any oxygen atom.
[0012] Preferably, the method does not comprise any
plasma-free post-treatment.
[0013] In a particular embodiment of the invention, the
fluorinated compound is a compound selected from the group
consisting of C6Fl4, C7F16r C8F18, C9F20 and C10F22i or mixtures
thereof.
[0014] Preferably, the fluorinated compound is
perfluorohexane (C6F14) .
[0015] In another preferred embodiment of the invention,
the fluorinated compound is of the type:
R1- N -R3
I
R2

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wherein R1r R2 and R3 are groups of the
perfluoroalkane type of formula CnF2n+1, or a mixture of these
compounds.
[0016] Preferably, the fluorinated compound is
perfluorotributylamine ((C4F9)3N) (CAS No. 311-89-7).
[0017] Preferably, the vapor pressure of said
fluorinated compound at room temperature is comprised between
1 mbar et 1 bar.
[0018] In a preferred embodiment of the present
invention, the partial pressure of said fluorinated compound
in said carrier gas is regulated by controlling the
temperature of a bath of said fluorinated compound into which
the carrier gas is injected before injection into the plasma.
[0019] Preferably, the temperature of the bath is
maintained at a temperature at which the vapor pressure of
said compound is less than 10 mbars, preferably less than 2
mbars.
[0020] In a preferred embodiment of the invention, said
fluorinated compound has a vapor pressure at 25 C, of less
than 10 mbars, preferably less than 2 mbars.
[0021] In a preferred embodiment of the invention, the
atmospheric plasma is produced by a device of the dielectric
barrier type.
[0022] In a preferred embodiment of the invention, the
atmospheric plasma is produced by a device of the type using
microwaves.
[0023] Preferably, the carrier gas is a gas having low
reactivity selected from the group consisting of: nitrogen and
a rare gas or mixtures thereof, preferably a rare gas or a
rare gas mixture, preferably argon.
[0024] In a particular embodiment of the invention the
substrate comprises a deposit surface comprising a polymer, in
particular PVC or polyethylene.

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[0025] In another embodiment, the substrate comprises a
deposition surface comprising a metal, or a metal alloy, in
particular steel.
[0026] In another embodiment of the present invention,
5 the substrate comprises a deposition surface comprising a
glass, in particular a glass comprising amorphous silica.
Description of the Figures
Fig. 1: general view of a system for deposition by atmospheric
plasma.
Fig. 2: sectional view of a cylindrical deposition system.
Fig. 3: XPS (X-ray Photoelectron Spectroscopy) spectra of the
sample treated in Example 2.
Fig. 4: detail of the XPS spectrum of the sample treated in
Example 2, carbon peak.
Fig. 5: illustrates the XPS spectrum of the non-treated PVC.
Fig. 6: illustrates the XPS spectrum of the non-treated
polyethylene.
Fig. 7: illustrates the XPS spectrum of the sample treated in
Example 4.
Fig. 8: illustrates the XPS spectrum of steel after cleaning,
and before deposition.
Fig. 9: illustrates the XPS spectrum of the sample treated in
Example 6.
Fig. 10: illustrates the XPS spectrum of the sample treated in
Example 8.
Fig. 11: illustrates the XPS spectrum of
polytetrafluoroethylene (PTFE).
Detailed description of embodiments of the invention
[0027] The present invention discloses a method for
depositing a fluorinated polymeric layer via a plasma
technology operating at atmospheric pressure. It allows
deposition of a fluorinated polymer layer via a fluorinated
compound which is injected into the plasma, or into the post-

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discharge area of the latter. In the selected example, the
monomer is a liquid at room temperature (25 C),
perfluorohexane, and is carried away into the plasma via a
carrier gas, argon. In the present case, the plasma is
generated in a discharge with a dielectric barrier, the sample
to be treated being placed inside the discharge, or at the
immediate exit of the latter (post-discharge).
[0028] In order to improve control of the deposition
thickness and reduce emission of fluorinated pollutant vapors,
the partial pressure of fluorinated compound in the plasma is
maintained at low values, preferably less than 10 mbars. This
low pressure is obtained either by maintaining the fluorinated
liquid at a low temperature, or by selecting a fluorinated
liquid having a vapor pressure of less than 10 mbars at room
temperature.
[0029] The use of these low concentrations of
fluorinated compounds within the plasma in particular allows
deposition of ultra-thin layers, with which transparent layers
may be obtained. Moreover, as the adhesive and wettability
properties are essentially related to interactions over very
short distances, the thinness of the deposition does not
degrade these properties.
[0030] The present invention further has the advantage
of allowing any surface to be treated insofar that the
geometry of the discharge is adapted and has the advantage of
proceeding in a single, simple and rapid step.
[0031] In a particular embodiment of the invention, the
fluorinated compound is of the type:
R1 - N - R3
(
R2
wherein R1r R2 and R3 are groups of the perfluoroalkane type,
of formula CõF2n+1. The advantage of such a type of molecule
lies in the weakness of C-N bond (2,8 eV of binding energy)

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relatively to the C-C bond (4,9 eV of binding energy)
promoting a fragmentation scheme of the precursor in the
plasma producing radicals =R1r =R2 and =R3, and, therefore,
allowing better control of the nature of the reactive species
within the plasma discharge and in the post-discharge area of
the latter. Surprisingly, the use of this type of molecule
induces the incorporation of a small amount of nitrogen into
the deposited film.
[0032] More particularly, long fragments improve the
properties of the deposited layers. Perfluorotributylamine
((C4F9)3N) in particular has exhibited excellent properties.
[0033] In the examples hereafter, the substrate consists
of a film of PVC (polyvinyl chloride), PE (polyethylene),
steel or glass, without this being limiting, it being
understood that for one skilled in the art this technology is
immediately transposable to any type of substrate.
Exemplary embodiments
Example 1
[0034] Example 1 shows a deposit of perfluorohexane on
PVC, achieved in post-discharge under the following
conditions:
A sample 3, as a PVC film of 4 cm x 4 cm of the Solvay brand
is cut out, cleaned with methanol and isooctane and placed at
the outlet (at 0.05 cm) of a cold plasma torch (Fig. 1)
(discharge with a dielectric barrier) operating at atmospheric
pressure. The fluorinated monomer (perfluorohexane) is placed
in a glass (Pyrex) bubbler immersed in a Dewar vessel
containing a mixture of acetone and dry ice. The temperature
of the mixture, and therefore of the monomer, is about -80 C.
The vapor pressure of perfluorohexane at this temperature is
about 1.2 mbars. An argon flow is then sent into the bubbler,
with an initial overpressure of 1.375 bars. The
argon/perfluorohexane gas mixture 1 is carried away into the

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inside of the torch. A plasma is initiated with a voltage of
3,200 Volts and a frequency of 16 kHz for 1 minute.
Example 2
[0035] Example 2 shows a deposit of perfluorohexane on
PVC produced in a discharge with a dielectric barrier under
the following conditions.
The sample is attached onto the inside of the external
electrode 9 of a discharge with a cylindrical dielectric
barrier. The << hot >> electrode 8, the one to which the voltage
is applied, is the internal electrode covered with an alumina
cup. Alumina cement provides the seal (Fig. 2).
The fluorinated monomer is brought into the discharge as in
Example 1. A treatment of 1 minute at a voltage of 3,000 V and
a frequency of 20 kHz is applied subsequently (treatment in
the discharge area).
The unambiguous presence of a fluorinated layer at the surface
of the PVC film is proved by X photoelectron spectroscopy. The
spectra of Figs. 3 and 4 illustrate full survey and
magnification of the carbon area. The presence of fluorine of
CF2 groups is clearly identified via the fluorine peak located
at 689 eV and the position of the carbon peak, 291.5 eV
actually corresponds to the carbon -CF2-.
The stability of the deposited layer is attested by the
preservation of the value of the contact angle after aging (in
air) for one week.
Example 3
Example 3 is identical with Example 1, except for the
substrate, which in this example is polyethylene.
Example 4
Example 4 is identical with Example 3, except for the
substrate, which in this example is polyethylene. The spectrum
of a PE sample (Fig. 6) contains a main peak around 285eV. It

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corresponds to the carbon (Cls) The presence of a peak of
low intensity is also noted around 530 eV, the latter
corresponds to contaminating oxygen.
[0036] After exposure to the plasma, the spectrum
includes two components (Fig. 7), one at 689.7 eV, F1s and the
other one at 292.1 eV, Cls, of the CF2 type. The calculated
composition is 61.2% of fluorine, 38.8% of carbon.
Example 5
In Example 5, a deposit of a fluorinated layer on a steel
substrate was made according to the same deposition procedure
as for Examples 1 and 3, except that the monomer this time was
perfluorotributylamine, the temperature of which was
maintained at 25 C. The vapor pressure of
perfluorotributylamine at 25 C is 1.75 mbars.
Example 6
[0037] In Example 6, a deposit of a fluorinated layer on
a steel substrate was made according to the same deposition
procedure as for Examples 2 and 4, except that the monomer
this time was perfluortributylamine, the temperature of which
was maintained at 25 C. The vapor pressure of
perfluorotributylamine at 25 C is 1.75 mbars, which allows it
to be used at room temperature.
[0038] After conventional cleaning, the steel surface is
still contaminated by oxygen and carbon. By slightly ion-
spraying the sample, it is possible to partly remove this
contamination (Fig. 8: XPS before treatment).
[0039] After exposure to the plasma, the XPS spectrum
includes 2 main components, the occurrence of a new component
of low intensity (Fig. 9) is also noted. The main components
are located at 689.7 eV (Fls) and 292.1 eV (Cls), of the CF2
type. The new component is located around 400 eV, it
corresponds to nitrogen (Nls). The calculated composition is
62.2% of fluorine, 33.3% of carbon and 4.5 % of nitrogen. The

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component due to nitrogen is only present when the monomer
containing nitrogen (C12F27N) is used.
5 Example 7
In Example 7, a deposit of a fluorinated layer on a glass
substrate was made according to the same deposition procedure
as for Example 5.
Example 8
10 In Example 8, a deposit of a fluorinated layer on a glass
substrate was made according to the same deposition procedure
as for Example 6.
[0040] As earlier, after exposure to the plasma, the
spectrum includes two main components, the occurrence of a new
component of low intensity (Fig. 10) is also noted. The main
components are located at 689.7 eV (Fls) and 292.1 eV (Cls),
of the CF2 type. The new component is located around 400 eV, it
corresponds to nitrogen (N1s). The calculated composition is
63.0% of fluorine, 32.8% of carbon and 4.2 % of nitrogen.
Example 9
A sample prepared according to Example 2, was subject to aging
for one week in the atmosphere, at room temperature.
Example 10 (comparative)
A PVC sample was exposed to an atmospheric plasma of argon, in
the post-discharge area, according to the same experimental
scheme as in Example 1, in the absence of the fluorinated
monomer.
Example 11 (Comparative)
A PVC sample was exposed to an atmospheric plasma of argon, in
the discharge area, according to the same experimental scheme
as in Example 2, in the absence of fluorinated monomer.
In Examples 1-9, the energy of the peaks as well as the
composition of the surface obtained after treatment are very

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close to the values obtained for a PTFE sample. Indeed, the
PTFE spectra (Fig. 11) shown in the literature also include 2
peaks, one at 689.7 eV corresponding to fluorine and the other
one at 292.5 eV corresponding to carbon (Cls). The
composition of the surface is 66.6 % of fluorine and 33.4 % of
carbon.
[0041] Table 1 shows the contact angles of water on the
surfaces of the different examples and on the surfaces of non-
treated substrates.
Contact angle of the water on the surface
PVC 81
Example 1 111
Example 2 111
PE 790
Example 3 111
Example 4 1110
Steel 78
Example 5 111
Example 6 111
Glass 35
Example 7 112
Example 8 112
Example 9 112
Example 10 40
Example 11 22
PTFE 105
Table 1
[0042] In all these examples, the deposited polymer
layers are perfectly transparent and invisible to the naked
eye.
[0043] The method may be applied to all cold atmospheric
plasmas, regardless of the energy injection method (not only
DBD, but RF, microwaves,...) .
[0044] The method may be applied to all surfaces which
have to be covered with a fluorinated layer: glass, steel,
polymer, ceramic, paint, metal, metal oxide, mixed, gel.
[0045] A hydrophobic layer may be deposited only if the
initial monomer does not contain any oxygen or hydrogen.

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Indeed, the presence in the plasma discharge, or in the post-
discharge area of oxygenated radicals directly induces the
incorporation of hydrophilic oxygenated functions into the
deposited layer on the one hand, the presence of hydrogenated
radicals generally induces their recombination with residual
oxygen or humidity, giving rise to the occurrence of 0H=
radicals, which are very hydrophilic, on the other hand.
Captions of the references in the figures
1 Fluorinated compound/ argon mixture flow
2 Generator
3 Sample
4 Alumina or metal electrode
5 Electrode covered with alumina
6 Copper support (grounded)
7 Copper electrode (grounded)
8 Internal mobile hot >> electrode
9 External metal electrode

Representative Drawing